1. Field of the Invention
The present invention relates to an optical recording method for recording information by holography, an optical recording apparatus using the method, an optical recording medium, an optical reproducing method, using the optical recording method. More specifically, the present invention relates to an optical recording method capable of effectively adjusting the amount of deviation of the optical axes of a plurality of laser beams, in which the deviation is attributed to variations in recording accuracy of an optical recording apparatus, upon recording or reproducing of information on or from an optical recording medium or focusing control and/or tracking control on the optical recording medium by means of the laser beams, and the present invention relates to an optical recording apparatus, an optical recording medium, and an optical reproducing method using the method.
2. Description of the Related Art
An optical recording method for recording information on an optical recording medium by holography generally involves interference of information light (object light) having image information with reference light in an optical recording medium to record a resultant interference fringe on the optical recording medium. An example of such an optical recording method is a collinear strategy in which information light and reference light are collinearly applied. In this collinear strategy an interference fringe is formed as a result of interference between the information light and the reference light, recording image information or the like in its recording layers. The recorded information is reproduced by applying reference light identical to that for recording from the same direction to thereby produce diffracted light from the interference fringe and by receiving the diffracted light.
Upon recording or reproducing of image information or the like, controls of light focus points (e.g., focusing and tracking controls) are carried out for recording/reproducing information on/from a proper position of an optical recording medium, by adjusting variations in distance within a layer (e.g., recording layer) in the optical recording medium and/or variations in recording accuracy of the optical recording apparatus.
As a method for adjusting focus points, for example, a sampled servo method is available. In the sampled servo method, servo light is applied on an optical recording medium for focusing and tracking, and reflected light is utilized to detect location information such as focusing information and/or tracking information for proper light irradiation. This focus point control allows application of the information light and the reference light on the exact location on the optical recording medium, thereby recording or reproducing information (see Japanese Patent Application Laid-Open (JP-A) Nos. 2003-151143, 2003-178456 and 2003-228875).
However, on the aforementioned focusing adjustment method, the detection is targeted only to the location information (e.g., the focusing information and the tracking information) of the servo light irradiation, and the applying location of the information light and the reference light in the recording layer is not regarded as a target of the detection. Therefore, there is a problem in the optical recording and reproducing apparatus which performs recording, reproducing, focusing control, and tracking control using a plurality of laser beams including not only information light and reference light, but also servo light as in the aforementioned positioning control method, such that even the focusing control or tracking control is performed, as shown in FIG. 3, the information is recorded in a location sifted from the proper location in the optical recording medium 20, when there is an error caused between the optical axis of a laser beam 33 for location control, such as servo light, and the optical axis of a laser beam 35 for recording and reproducing (gap between the optical axis of the laser beam 33 and the optical axis of the laser beam 35) at the time of manufacturing process, as shown in FIG. 1. Ideally, the optical axis of the laser beam 33 and the optical axis of the laser beam 35 are applied at the appropriate reproduction location, namely being applied collinearly, as shown in FIG. 2.
In the case where the aforementioned gap (also referred as “deviation” hereinafter) is large when the optical recording medium 20 in which the recorded location is sifted as shown in FIG. 3 is reproduced by means of another optical reproducing apparatus, or in the case where there is a gap, i.e., deviation between the optical axes of the reproduction light 35 and servo light 33 for use in the optical reproducing apparatus as shown in FIG. 4, the reproduction light 35 is not correctly applied to the information recorded part (the oblique lined portion in FIG. 4) in the optical recording medium 20, and thus the information recorded on the optical recording medium 20 cannot be reproduced.
Therefore, in the same optical recording and reproducing apparatus, even if the recording and reproducing can be properly performed on one optical recording medium, the reproducing may not be properly performed on another optical recording medium, and thus there is a problem in compatibility, such that the adjustment of the optical recording and reproducing apparatus is required. Since there is a limitation in reducing an error of the optical recording and reproducing apparatus, the manufacturing cost may be increased as a result of seeking such the highly accurate optical recording and reproducing apparatus.
Therefore, there are not yet realized an excellent optical recording method, optical recording apparatus, optical recording medium, and optical reproducing method, which are capable of efficiently adjusting the deviation of the optical axes of the plurality of the laser beams caused by an error or the like of the optical recording, and optical reproducing apparatuses when recording, reproducing, focusing control or tracking control is performed by the plurality of laser beams on an optical recording medium which is recorded by holography. Accordingly, it is strongly desired to provide such that optical recording method, optical recording apparatus, optical recording medium, and optical reproducing method.